Chemical removal of an acid-soluble metal part in a deep well



, Feb. 17, 1948. H. CARDWELL ETAL 2,436,198

CHEMICAL REMOVAL AN ACID-SOLUBLE METAL PART IN A DEEP WELL Filed Aug. 6,1945 I I .I

IN ll 8 I l l I 2 1 I 5 7 x i INVENTORS Pay/H Carowe// By Louis H Ef/ersATTORNEYS Patented Feb. 17, 1948 @HEMICAL REMOVAL OF AN ACID-SOLUBLEMETAL PART IN A DEEP WELL Paul H. Cardwell and Louis H. Eilers, Tulsa,

Okla, assignors to The Dow Chemical Com.- pany, Midland, Mich, acorporation of Delaware Application, August 6., 1945,. Serial No.609,254 1 Claims. (01. 252-855) 1 The invention relates to the chemicalremoval of an acid-soluble metalpart in a deep well. It moreparticularly concerns an improved method of completin wells, traversinga plurality of strata, in which a chemically soluble casing sectionlocated opposite a selected stratum is removed by chemical action topermit fluid flow between the well bore and the stratum.

In the usual well completion in which a chainlcally soluble section isincluded in the casing string opposite a productive zone, the solublesection is made of aluminum or an aluminum alloy, and its removal iseffected by prolonged treatment with a quantity of hydrochloric acid.

A disadvantage of this method which limits its usefulness is that theaction of the acid is quite slow, so that an inordinate amount of timeis consumed in the operation and complete removal is somewhat uncertain.Y

A particular object of the invention is to provide an improved methodof, and composition for, chemically dissolving an aluminum or aluminumalloy part, such as a casing section, in the bore of a well wherebycomplete rapid removal is achieved. Other objects and advanta es willbecome. apparent as thedescription of the invention proceeds.

According to the invention dissolution of parts or equipment made ofaluminum or aluminum alloy in the well is achieved by subjecting themetal part to the corroding action'of a hydrochloric acid solution towhich has been added a relatively small amount of .a phosphorus acid,such as phosphoric acid (H3PO4) and hypophos phorous acid (H(H2PO2)).To'prevent or reduce attack by the acid solution on adjacent ferrousmetal parts, when such are present, an inhibitor of such action may beincluded in the acid solution.

The invention may be more readily understood from the following detaileddescription and accompanying drawing of a mode of carrying out theinvention, such mode illustrating but one of various ways in which theprinciple of the invention may be used. In the said drawingthe singlefigure illustrates schematically in vertical section an oil well inwhich an acid-soluble section located in the casing string opposite aproductive zone is being removed chemically.

Referring more particularly to the drawing, the well bore l is providedwith a casing. string 2 containing an aluminum alloy (acid-soluble)section 3. Various aluminum-base alloys are suitable for the purpose as,for example, one containing about 1 per cent of silicon, about, 1 percent of magnesium, and about 0.3 per cent of chromium, the balance beingaluminum. If desired, unalloyed aluminum may be used. The aluminum oraluminum alloy section is placed in the casing string so that thesectionis op- 2 posite a productive zone 4, the annular space betweenthe casing string and the well hole being filled with cement 5. Suchwell construction is conventional and forms no part of the invention.

In preparing the well for treatment so as to remove the soluble section3 according to the inventiomthe portion of the well below the productivezone 4 is bridged as with a filler 6, and a packer 1' is set in thecasing at the top of the zone thereby to isolate for treatment theportion of the well containing the soluble section. The packer isprovided with a central passage for admitting the outer tube 8 extendingfrom the top of the well to just below the packer. An inner tube 9' isstrung through the outer tube and extends from the top of the well tonear the bottom of the soluble section.

After arranging the apparatus as described. the chemical solvent ofhydrochloric acid to which has been added a suitable phosphorus acid maybe, introduced through tube 9 so as to fill the space ID in the casedportion of the well between the top of the bridge 8 and the bottom ofthe tube 8. ,As the chemical solvent becomes spent by dissolving themetal of the soluble section 3 of the casing, fresh solvent maybeintroduced,

if necessary, thereby'displacing the spent solution from the wellthrough tube 8 It is referable to continuously circulate the chemicalsolvent into the space I0 through tube 9 while the spent or partiallyspent solvent solution is displaced through tube 8. The amount ofsolvent to employ depends upon the concentration of HCl therein and theWeight of the aluminum section to be removed, and may be computed on thebasis of the known stoichiometrical relationship between HCl andaluminum to form aluminum chloride (A1013). For example, approximately1.7 gallons of 25 per cent hydrochloric acid solution is required perpound of aluminum section. Various concentrations of HCl may be used,such as 10 to 35 per cent, concentrations between about 15 and 20 percent being preferred.

A convenient way to introduce hypophosphorous acid into. thehydrochloric acid solution is to employ a solublev salt ofhypophosphorous acid, such as sodium hyp p p (NaH2PQ2)- A suitableamount of the hydrated salt,

NaHzPOzHzq may be dissolved in the hydrochloric acid solution which thenbehaves in the same manner as when hypophosphorous. acid itself is used.Preferred proportions of sodium'hypophosphite or hypophosphorous acid touse are between about 0.1 and 2 per cent of the weight of thehydrochloric acid solution; those of phosphoric acid are between about0.5 and 2 per cent.

In order to reduce or prevent attack by the acid on the ferrous metalparts of the well which 3 may be exposed to the acid solution,particularly the steel casing adjacent to the acid-soluble part to beremoved, any of the well known corrosion inhibitors may be used, such asa soluble-' arsenic compound, e. g., the arsenate or arsenite of sodium,organic sulfur compounds, such as the mercaptans, organic nitrogenbases, etc., in' I generation of heat is an advantage as it speeds.

the reaction.

After the aluminum section has been removed, the packer I and tubingstrings 8 and 9 are removed so as to permit drilling out the cementsheath II opposite the zone 4 and removal of the bridge 6, if desired,

- As illustrative of the increased rate of action of hydrochloric acid naluminum alloy tubing brought about by the addition of a corrosionaccelerator of a phosphorus acid, tests were made in which pieces of thetubing were subjected to the dissolving action of hydrochloric acidsolution to which the aluminum corrosion accelerator was added. Inconducting these tests 300 cc. lots of acid solution were placed in acalorimeter together with a piece of an aluminum alloycontaining 0.2 percent copper, 1 per cent magnesium, 0.4 per cent silicon, 0.2 percentchromium, the balance being aluminum, and the rate of dissolving of thealuminum alloy determined by observing from time to time the temperatureattained by the reacting materials. In these tests the higher thetemperature attained by the materials in a given number of minutes afterthe reaction begins the faster the dissolving of the aluminum alloyoccurs. Tables I and II present data so obtained.

TAsLa I Rate of reaction of hydrochloric acid solutions on aluminumalloy Rate of reaction of hydrochloric acid solutions on aluminum alloyTemperature F.) of Reacting Materials After Composition of Acid Solutioni Min. Min. Min. Min. Min.

% HCI (Blank) 86 109 162 220 220 20% 0.5% HiPOi. 86 107 168 213 20% 0.5%NEHgPOz.-. v 86 150 216 218 216 The data in the tables show that byadding a phosphorus acid in relatively small amount to hydrochloricacidsolution its rate of'attack'lon aluminum alloy is' increased; Thisisevident from the fact that the temperature of the reacting materialsattains a higher value in less time when a phosphorus acid is present inthe acid solution.

The term aluminum used herein and the appended claims is used to meanall grades of aluminum metal, and the term aluminum alloy means alloysof aluminum containing at least about per cent of aluminum.

We claim:

1. A composition for dissolving a metal part formed of aluminum and itsalloys which comprises hydrochloric acid containing from about 15 to 20per cent of HCl and 0.1 to 2 per cent of hypophosphorous acid.

2. A composition for dissolving a metal part formed of aluminum and itsalloys which comprises an aqueous solution of hydrochloric acidcontaining from about 15 to 20 per cent of HCl to which has been added0.1 to 2 per cent of sodium hypophosphite.

3. The method of removing from a well ametal part formed of aluminum andits alloys which comprises subjecting the part to the dissolving actionof an aqueous solution comprising hydrochloric acid containing fromabout 10 to 35per cent of HCl and 0.1 to 2 per cent of a phosphorus acidselected from the group consisting of phosphoric acid andhypophosphorous acid.

4. The method of removing from a well a metal part formed of aluminumand its alloys which comprises subjecting the part of the dissolvingaction of an aqueous solution comprising hydrochloric acid containingfrom about 10 to 35 per cent of HCl and 0.1 to 2 per cent of-aphosphorus acidselected from the group consisting of phosphoric acid andhypophosphorous acid and an inhibitor of the action of hydrochloric acidon ferrous metal.

5. The-method of removing from a well a metal partformed of aluminum andits alloys which comprises subjecting the part to the dissolving actionof an aqueous solution comprising hydrochloric acid containing fromabout 15 to 20 per cent of HCl and 0.1 to 2 per cent of hypophosphorousacid. r 6. The method of removing from a well a metal part formed ofaluminum and its alloys which comprises subjecting the part to thedissolving action of an aqueous solution comprising hydrochloric acidcontaining from about 15 to 20 per cent of HCl to which has been added0.1 to 2 per cent of sodium hypophosphite..

'7. The method of removing from a well a metal part formed of aluminumand its alloys which comprises subjecting the part to the dissolvingaction of an aqueous solution comprising hydrochloric acid containingfrom about 15 to. 20 per cent of HCl and 0.5 to 2 per cent of phosphoricacid. PAUL H. CARDWELII LOUIS H. EILERS. 1

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

